The invention relates to a method for cleaning particle filters in exhaust gas systems of combustion engines, in particular diesel engines in vehicles.
Given the increasing requirements on environmental and climatic compatibility, an increasing number of vehicles, especially those operated with diesel engines, are nowadays being fitted with particle filters, these generally being arranged in the exhaust gas system after the catalytic converter in order to filter incompletely burnt fuel in the form of soot and soot agglomerates out of the exhaust gas. By its very nature, a particle filter of this kind becomes clogged in the course of its operation since it is blocked to an increasing extent by the soot particles retained. It is therefore necessary to regenerate the particle filter from time to time.
In general, the particle filter on vehicles is regenerated by operating the engine at increased load, leading to an increase in the exhaust gas temperature in the particle filter. The effect of this increase in the exhaust gas temperature is that the soot particles retained are subsequently burnt in the soot particle filter, thereby freeing the particle filter again. In the case of vehicle engines, passive regeneration of this kind is carried out at high speed during freeway journeys, for example.
However, if a vehicle is mainly used only in an urban environment or for short distances on country roads, with the result that passive regeneration of the particle filter does not take place for a prolonged period, active regeneration has to be carried out, and this takes place when an appropriate sensor system, e.g. in the pressure sensor before and after the particle filter, detects that the throughput through the filter is becoming too low, i.e. that the filter must be regenerated.
Thus if the engine control system ascertains that active regeneration should be carried out, the engine injection point is retarded for this purpose, for example, and this also leads to an increased exhaust gas temperature in the particle filter since in this case the fuel is also burned in the exhaust gas system. This increase in the exhaust gas temperature also leads to burning of the retained soot particles, i.e. of the incompletely burnt fuel in the particle filter.
If regeneration still does not take place, owing to driving conditions for example, the driver is requested to visit a service garage. The service garage can intervene manually by electronic means to make the engine control unit carry out a regeneration.
However, this method is possible only up to a certain loading condition. If this “manual” regeneration is no longer possible, the usual practice nowadays in this case is to replace that part of the vehicle's exhaust gas system which contains not only the particle filter but also the catalytic converter. At best, the only choice remaining for the operator of the vehicle is between buying a brand new particle filter or a reconditioned particle filter together with the corresponding exhaust gas system subassembly, but in either case this leads to considerable costs for the vehicle operator.